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The influence of climate on mental health was considered unknown until not too long ago. Many experts denied this link out of sheer caution; they preferred to remain silent due to the lack of scientific evidence. Over the years, research has intensified, and now many of the statements that were the fruit of popular wisdom can be taken for granted.
In the opinion of Manuel Martín Carrasco, vice president of the Spanish Society of Psychiatry and Mental Health, the difficulties involved in carrying out studies that addressed the issue led to “very erratic results”. The main obstacles are the need for “very large population groups and the great variability of climatic conditions”.
However, according to the psychiatrist, “from the beginning of the 21st century, there was a significant increase in climate studies, related above all to climate change.” On the other hand, the concept of comprehensive health, which previously included biological, psychological and social aspects (the biopsychosocial model), has incorporated an environmental or ecological aspect. “The environment has begun to be considered as one of the causes of health in general and mental health in particular,” he summarises. In short, there is a growing consensus on the existence “of an association between climatic circumstances and mental health”.
Seasonal changes and mood
The influence of seasonal mood changes is, according to psychiatrist Pablo Pérez Gómez, from the Bipolarity Unit of the Clínica Nuestra Señora de la Paz of the Hospitaller Order of San Juan de Dios, “an area in which there is more and more scientific evidence. However, he warns that “there is also still a lot of research to be done.”
The paradigm of this link between a specific climatic situation and mental health would be the seasonal pattern of major depressive disorder, also called seasonal affective disorder. “In this disorder, depressive symptoms appear regularly in a certain year’s season, mainly in winter, although in some people, they may appear in spring or summer. It is believed that the main factor involved in this disorder is sunlight. “An effective treatment is phototherapy, in which the patient is exposed continuously to a light source of a certain intensity,” he adds.
On the other hand, in bipolar disorder, it has been observed that the seasonal pattern is especially frequent, “being able to affect a quarter of diagnosed patients”. However, the association between the appearance of depressive episodes in autumn-winter observed in the general population is repeated. On the other side of the coin, a greater appearance of episodes of mania and hypomania (excessive euphoria) has been observed in spring-summer.
Influence of light on mood disorders
Sunlight is one of the weather factors most closely linked to mental illness. At this point,” studies indicate a greater tendency to depression in more northern latitudes and also in colder and rainier areas within the same country.” However, in European epidemiological studies, “the Scandinavian countries do not stand out, especially as the countries with the highest prevalence of depression”. This is because climatic conditions “are among the many sociological, population and institutional factors that influence mood.”
In other mental illnesses, such as schizophrenia, there is no pattern of seasonality and relationship with light as clear as that observed in affective disorders. However, “there are studies that reveal an increase in hospital admissions due to relapses in people with schizophrenia in periods of high temperatures”.
Relationship between heat and hospital admissions in psychiatry
The link between elevated temperatures and increased hospitalisations extends to all mental illnesses. According to a study published in 2021 in Plos One on almost 89,000 admissions of patients due to the worsening of their psychiatric pathology between 1973 and 2017 in a hospital in Bern (Switzerland), the risk of hospitalisation increased linearly by 4% for each increase of 10 ° C in the average daily temperature.
In general, excessively high temperatures “are associated with a deterioration of both physical and mental health,” one need only look at the increase in mortality after a heat wave.
The rise in environmental temperature is especially associated with a greater presence of symptoms of anxiety, stress, depression, and irritability. “There are also studies that reveal that high temperatures are related to an increase in suicide rates, but in this case, the results are less consolidated”, points out the vice-president of the Spanish Society of Psychiatry and Mental Health.
The expert clarifies that the biological mechanisms involved in the impact of high temperatures on psychiatric disorders are still not well understood. “Some studies suggest that alterations in thermoregulation and the neurological response to heat can affect mental health”, he indicates.
The effects of cold on mental disorders do not seem clear: “Areas with very low temperatures are usually unpopulated or sparsely inhabited, and the most populated cities have a long tradition of exposure to cold and are more adapted.”
Instead, rising heat is an emerging problem due to climate change, and the populations facing it are less prepared because it is a new phenomenon.
Impact of climate disasters
Extreme weather events, such as hurricanes, cyclones, floods, fires or droughts, have a clear impact on mental health, but a large part of their effects occur indirectly. First of all, they are catastrophes that generate anxiety and post-traumatic stress.
“You also must consider the economic damages that derive from this situation,” adds Martín. These monetary difficulties trigger, in turn, discomfort, psychological problems and aggravation of already established psychiatric pathologies.
